1. Field of the Invention
The present invention relates to a method for manufacturing an SOI substrate having a semiconductor layer formed over an insulating film and a method for manufacturing a semiconductor device.
2. Description of the Related Art
Background Art
In recent years, instead of a bulk silicon wafer, integrated circuits using an SOI (silicon on insulator) substrate have been developed. By utilizing the characteristics of a thin silicon wafer formed over an insulating film, semiconductor layers of transistors formed in the integrated circuit can be separated from each other completely. Further, since the fully depleted transistors can be formed, a semiconductor integrated circuit with high added value such as high integration, high speed driving, and low power consumption can be realized.
Known examples of SOI substrates are SIMOX substrates and bonded substrates. For example, an SOI structure of a SIMOX substrate is obtained by implantation of oxygen ions into a silicon wafer and by heat treatment performed at equal to or higher than 1300° C. to form a buried oxide (BOX) film, whereby a silicon wafer is formed on a substrate surface.
As an SOI structure of a bonded substrate, two silicon wafers (a base substrate and a bond substrate) are bonded to each other with an oxide film interposed therebetween, and one of the two silicon wafers (the bond substrate) is thinned on its rear side (which is a surface facing a bonded surface), so that a silicon wafer is formed. There is proposed a technique which employs hydrogen ion implantation that is called a hydrogen ion implantation separation method (e.g., Reference 1: Japanese Published Patent Application No. H5-211128), because it is difficult to form a uniform silicon wafer by grinding or polishing. The hydrogen ion implantation separation method is also called a Smart Cut (registered trademark) method.
A summary of a method for manufacturing this SOI substrate is described. By implantation of hydrogen ions into a silicon wafer by an ion implantation method, an embrittlement region is formed at a predetermined depth from the surface of the silicon wafer. Next, a silicon oxide film is formed by oxidizing another silicon wafer which serves as a base substrate. Then, the silicon wafer into which the hydrogen ions are implanted is bonded to the silicon oxide film of the other silicon wafer which serves as a base substrate, so that the two silicon wafers are bonded. Then, through heat treatment, the silicon wafer is cleaved using the ion implanted layer as a cleavage plane, thereby forming a substrate in which a thin single crystal silicon layer is bonded to the silicon wafer which serves as a base substrate.
An ion implantation method is a method in which particles to be implanted into a sample in vacuum are ionized and accelerated by an electric field. An ion implanter used in an ion implantation method includes an ion source, a mass separation unit, an acceleration unit, a beam operation portion (electrostatic scan) unit, an implantation chamber (end-station), and an evacuation unit. Further, since a cross section of an ion beam is not uniform, scanning with an ion beam is performed electrically in order to obtain uniformity of a surface of the sample. The implanted particles have a Gaussian distribution in the depth direction.
In addition, a method for manufacturing a semiconductor device using the Smart Cut method, in which a highly heat-resistant substrate is used as a supporting substrate, is disclosed as an example of a semiconductor device using an SOI substrate (see Reference 2: Japanese Published Patent Application No. 2000-012864).